Treatment with thiamine hydrochloride and astaxanthine for the prevention of yolk-sac mortality in Baltic salmon fry (M74 syndrome)

Two practical methods are reported for treating feral Baltic salmon with th iamine hydrochloride against M74 syndrome (abnormally high yolk-sac fry mor tality of the Baltic salmon). Both bathing of the yolk-sac fry in thiamine hydrochloride (1000 mg l(-1), 1 h) and a single intraperitoneal injection g iven to the female brood fish (100 mg kg(-1) fish) during the summer 3 mo b efore stripping were shown to elevate the whole body total thiamine concent ration in the fry. Both treatments were also shown to be effective in preve nting mortality due to M74 syndrome. The effect of bathing the yolk-sac fry was shown to be dose-dependent. The results support the view that there is a causal relationship between the thiamine status of the yolk-sac fry and M74 mortality. An intraperitoneal injection of astaxanthine suspension admi nistered to the female brood fish (11 mg kg(-1) fish) in the summer 3 mo be fore stripping elevated the astaxanthine concentration in the eggs but did not affect mortality due to M74 syndrome. An interaction between astaxanthi ne and thiamine may occur in the developing embryo or yolk-sac fry, however . No association could be demonstrated between the various thiamine hydroch loride treatment practices and hepatic cytochrome P450 dependent 7-ethoxyre soruffin-O-deethylase (EROD) activity in the yolk-sac fry. An injection of thiamine hydrochloride into the peritoneal cavity of wild Baltic salmon fem ales could be used to raise thiamine concentrations in their offspring in t he rivers. The effect on smolt production in Finnish Baltic salmon rivers n eeds to be investigated further, however.